Making carbohydrate foods resistant to microorganisms



Patented June 28, 1949 MAKING CARBOHYDRATE FOODS RESIST- ANT TO MCROORGANISMS Gerald B. Coleman and Paul A. Wolf, Midland, Mich, assignors to The Dow Chemical Com pany, Midland, Mich a corporation of Delaware No Drawing. Application January 13, 1947, Serial N0. 721,877

1! Claims.

This invention relates to a method for imparting to foods rich in carbohydrates increased resistance to attack by microorganisms such as fungi, yeasts and bacteria, and to the so-treated products. It relates especially to a method for imparting such increased resistance to baked goods, and in particular to breadstufis.

It is a matter of common knowledge and experience that foodstuifs rich in carbohydrates (1. e., those containing 50 per cent or more of carbohydrate based on the total weight of protein plus fat plus carbohydrate) are subject to attack by such varied types of microorganisms as fungi,

yeasts and bacteria. The growth of such microorganismsis by no means universally injurious to the foodstuifs, but may give the food an unpleasant appearance or an unnatural flavor which may make the product unsalable or unpalatable to I the consuming public. Various materials have been suggested as inhibitors of such uncontrolled growth of microorganisms in foods rich in carbohydrates, but none are as successful as may be desired. Some prior inhibitors are short-lived in their eifect, and others require such high concentrations as to be uneconomical. Some are too selective for general use. Others contribute a distinct and undesirable flavor to foods. Some" are toxic and cannot be used safely in foods for human consumption. Most of the prior inhibitors modify the pH of the foods, or require particular pH conditions for antimicrobial eifeetiveness, and this makes them dimcult to use and tocontrol.

Purely by way of illustrating the diversity of foodstuffs which are rich in carbohydrates and which are subject to attack by fungi, yeasts and bacteria, the following partial list is given: baked goods,'including various wheat, rye and barley breads. cakes, cookies, crackers, oatmeal and oat flour." breads and crackers, soya ,flour products,

ginger bread, cornmeal products, rice flour prod-' ucts, and the-like; prepared cereal foods, including the predominantly cereal animal foods; yams, potatoes; turnips, carrots, beans and other vegetables commonly stored for long periods; vegetable and fruit Juices, including tomato Juice, prune juice, apple juice, grape Juice and the like; confections, candies, sweet chocolate such as "hot fudge sauce" and chocolate syrup, and the like; sorghum, molasses, maple sugar and syrup, corn syrup, cane sugar syrup, honey; carbonated and uncarbonated sweetened beverages containing fruit and root extracts; strawberries, grapes, citrus' fruits. and the like; jams, jellies and preserves; and numerous. others. It is not to be inferred that the foregoing and related foods are 2 invariably attacked and made unacceptable for table use, but it should be understood that each of them is subject to such microbial attack and that the extent of the damage done will depend largely on the history of the particular product concerned, the conditions under which it is prepared and stored, and upon the kind and amount of antimicrobial agent, if any, with which it may be treated. In any case, it is desirable that a resistance to attack by microorganisms be imparted to foods rich in carbohydrates, and that the means employed be itself an odorless, tasteless, non-injurious, edible material.

' odorless.

It is accordingly among the objects of the present invention to provide amethod for imparting to foods rich in carbohydrates anincreased resistance to attack by'microorganisms such as fungi, yeast and bacteria. A related object is to provide such a method, in which the means employed to impart the said resistance is an odorless material which is tasteless at use concentrations and is both non-injurious to the foods and edible by humans. A particular object is to provide a method for imparting to baked goods, especially to breadstufls, an increased. resistance to attack by microorganisms after the baking operation. Another object is to provide a method of using particular compounds to impart to carbohydrate-rich foods an improved resistance to attack by microorganisms. A further object is to I provide carbohydrate foods having improved resistance to such attack.

The present invention is dependent upon the heretofore unknown and surprisingly high antimicrobial properties (as regards organisms whose growth is normally fostered by foods rich'in carbohydrates) of the chemical compound known as dehydroacetic acid and its edible salts. Dehydroacetic acid, which has the structural formula I H|C-C 0:0 0

rt- -cm is also known as 3-acetyl 6-methyl pyrand1one-2A, and exists in both a keto and an enolic form. Dehydroacetic acid and its sodium, potassium, ammonium and calcium salts are non-hazardous to humans at use concentrations, and in the amounts usually employed are both tasteless and They are essentially neutral compounds, and do not affect materially the pH of foodstuifs in or on which they are employed in the invention. Dehydroaeetic acid is slightly soluble in water and is readily soluble in alkalies and a variety of organic solvents, including ethyl alcohol and the glycols, and may be deposited mum concentration of the antimicrobial agent which allows growth to proceed normally, while the second or right-hand numeral represents the minimum concentration which fully inhibits mifrom or used in such of these solutions as is crobial growth onasuitable nutrient agar medium deemed appropriate for the particular case. in a petri dish. Both values are given as a per Dehydroacetic acid is slightly more efieetive (i. e., cent by weight or the medium.

Table Microbistat', Per Cent owl-3m Dehydro- Dichloro- Calcium Sodium Propionie Benzoic acetic acetic Acid Propionate Propionate Acid Acid Acid p115 p118 pHB pH5 p116 Penicillium digitalum 0.01' 0.025 5.0 5.0 5.0 an 5.0 0.1 0.25 0.1 0.5

Sacchcromyce urevin'ae. 0.01 0.025 5.0 7.5 7.5 0.75 1.0 0.25 0.50

Penicilliam apanmm. 0.0075 0.01- 5.0 7.5 7.5 0.25 0.50 0.1 0.25

Agperpillul nicer 0.025 0.05 5.0 a.0 r 5.0 1.0 0.25 0.50 0.50 0.15

Ladobocilluaplaniamm- 0.03 0.10 0.5 0.15 1.5 1.5 1.0 2.0 0.25 0.50

mizopucnigricam 0.0 0025- 5.0 6.0 75 3.0 5.0 0.25 0.50 0.25 0.50

it may be used at slightly lower concentrations) Other organisms of numerous types respond in in neutral or acid media than in an alkaline the same manner, and are controlled at similar medium, and when high solubility in aqueous concentrations of dehydroacetic acid. These in media is required, the neutral sodium salt is elude, for example, Aerobacter aerjogenes, Erwinia recommended. caratovora. Fusarium ozysporium, Phomopsis The method of the invention may be defined citrii, Sclerotium roljsii, Bacillus mesentericus,

as one for imparting to foods rich in carbohyand the like. The foregoing table shows that dedrates an increased resistance to attack by microhydroacetic acid is usually at least as effective organisms which comprises bringing into close as ten times its weight of other representative association with such foods a compound selected commercial antimicrobial agents. Less of the from the class consisting of dehydroacetic acid dehydroacetie acid will be required in any parand its edible salts. The term edible salt" as ticular application than of the other agents, and herein used refers to those salts of dehydroacetic in s0me eases the other agents are not efi'ective acid which may be ingested by humans in the at any practical concentration. small amounts present in foods containing them, without harmful efiect. The requisite close asso- EXAMPLE? 2 elation m y be obtained by incorpor the Dehydroacetic acid was mixed in various prodehydroacetic acid compound in the food. by 40 portions with whole-wheat flour. A standard applying it to the exterior of the foo by bread dough was prepared from each of the mix-- wrapping the food in a wrappe i a m g the tures. Since the tests in vitro reported in Excompound, as may be most appr p fl the ample 1 had indicated that dehydroacetic acid type of food to be treated. Owing to its easily inhibits growth of S. cerevisiae. the yeast erately low volatility, the antimicrobial effect of a used t maven bread, there was concern as to d hy ct c a is of 10118 duration, even in whether the bread would rise, and if so, whether those cases in wh ch it is applied externally of it would exhibit any practical degree of protec-. the food, and is exposed to the atmosph While tion against A. niger, R. niqricans, and B. mesene the amount of dehydroaeetic acid, or salt thereof, t i common bread contaminants. It was to be used may vary considerably, d pe 0!! found that at 0.3 per cent concentration, based the type of food to which it is to be applied and the conditions and microorganisms which the food may be expected to encounter, a significant measure of resistance to attack is found to be imparted to carbohydrate rich foods through the use of 0.01 to 0.5 per cent of dehydroacetic acid, based on the weight of food, and that fungusrepressing wrapping sheets need not contain over 10 per cent, and may conveniently contain less than 5 per cent by weight of dehydroacetic acid.

The following specific examples illustrate the practice of the invention, but are not to be construed as limiting the invention either to the foods specifically disclosed or to the microorganisms whose growth is shown to be repressed.

EXAMPLE 1 The antimicrobial spectrum of dehydroacetic acid has been determined to be very comprehensive. In the following table appear the results of tests in vitro to i lustrate the relative effectiveness of dehydroacetic acid and some of the previously known antimicrobial agents against a few typical organisms. In each column, the

' first or left-hand numeral represents the maxion the weight of the baked loaf, dehydroacetic acid partially inhibited the growth of the yeast, and that the resulting loai' had some fiat" spots At concentrations up to at least' 0.2 per cent, dehydroacetic acid does not show any effect on the leavening action of the yeast. The baked loaves, including some containing no dehydroacetic acid, were each partially sliced, and were exposed continuously to the atmosphere at a temperature of to F., and a relative humidity of 90 to per cent. These extreme conditions, most tavorable to mold growth, produced heavy growths of mold on the untreated bread in two or three days. Amounts of dehydroacetic acid up to 0.06 per cent of the weight of the bread retarded but did not completely inhibit mold growth, while concentrations above about 0.10 per cent not only retarded but inhibited mildew, even -under the rigorous conditions of the test, for as much as 14 days. Under the milder conditions of normal bread storage. the antimicrobial effect of dehyq droacetic acid is even more prolonged. and the comparison with untreated bread is more favorable to the present'agent, if that is possible. In no case was it possible to detect any diflerence in taste between the freshly baked treated and untreated loaves.

The seemingly preferential inhibition 01' mold, as compared with yeast, in bread, is probably due to the relatively small number oi. mold spores that gather on the bread and make it unacceptable for table use in comparison to the large yeast inoculum which is used in bread making. Enough of the yeast can grow to leaven the bread, but the mold contaminant is not permittedtomatlire.

Similar, results obtain with white" and with rye' bread, inhibition resulting from the use of 0.08 per cent or more of dehydroacetic acid in the bread. Amounts greater than 0.2 per cent of the agent were not found necessaryin any bread product, to obtain the required protection.

EXAMPLE 8 Various amounts of dehydroacetic acid were mixed with" a. commercial ready-mixed gingerbre'ad powder. The directions supplied by the manufacturer were followed and the gingerbread was baked, cut, and then exposed for 14 days at 85 F. in an atmosphere having 90 to 100 per cent relative humidity. For comparison, a similar series of gingerbreads was prepared using calciumpropionate as the additive, since it is being supplied commercially as a iungistat. The re- Under identical conditions, dehydroacetic acid is seen to be about times as eifective as calcium propionate. EXAMPLE 4 The neutral sodium salt of dehydroacetic acid, dissolved to the extent of 0.05 per cent by weight in fresh cider and apple juice eflectively inhibitedthe'grow'th of molds and of fermentation and oxidative organisms, and the product remained "sweet and clear for a prolonged period. An untreated control, in the same period of time. developed a pellicle over its entire surface, and smelled strongly of vinegar.

Exams: 5

Commercial samples of a thick chocolate "hot fudge syrup and of a more .fluid chocolate syrup. bothoi which were sweetened to be predominantly "carbohydrate foods, and both of types which are used as ice cream additives. were v llixmptnd Various commercial syrups used for sweetening purposes, including corn syrup (glucose), honey, maple syrup, molasses and cane sugar syrup are subject to the growth of contaminating molds. The same is true of the flavoring syrups used in confectionery, in carbonated beverages, and in ice cream products. The addition of 0.025 to 0.05 per cent by weight of dehydroacetic acid to such syrups effectively inhibits such growths and does not affect the flavor of the syrups. Thus, in one series of tests. a commercial molasses was inoculated with a small amount of moldy syrup, and was divided into several portions. One portion was set aside as a control and the others were treated with from 0.01 to 0.1 per cent by weight of dehydroacetic acids A heavy growth of bluewhite mold appeared in the control, while all samples containing 0.025 per cent or more of dehydroacetic acid remained free from mold.

Exaurnrr they may become badly mildewed. Such growth appears to'originate at and to spread from the injured spots. It has now been found that the contaminating growth of mildew can be minimized on strawberries, raspberries, blackberries, loganberries, huckleberries (blueberries), and the like. by dipping the freshly picked fruit in a solution of 0.1 per cent by weight of dehydroacetic acid in water. In one specific case, strawberries, which had been picked from 24 to 36 hours previously and which had not been refrigerated, were dipped in 0.05 and 0.1 per cent solutions of dehydroacetic acid. An untreated-control was entirely blanketed with mildew after exposure to air at F. for an additional 5 days. and the fruit was obviously decomposing. The berries treated with the 0.05 per cent solution had a few visible colonies of mildew, but smelled fresh and sweet. The berries dipped in the 0.1 per cent solution were substantially as fresh and edible as when purchased. When the treatment follows immediately after picking, the results are even more favorable.

EXAMPLE 8 Sliced loaves of commercial baker's bread were sealed in the usual manner in'various types of bread wrappers. Some of the wrappers were untreated, others were purchased as being fungistatic, and the remainder were paper sheets which had been impregnated with 2 per cent by weight treated with various amounts of dehydroaceticacid and were exposed to the atmosphere at 85 F. 'The untreated controls showed considerable mold growth on the exposed surfaces in a week. No such growth appeared in 20 days on the "hot fudge samples containing 0.05 per cent or more otdehydroacetic acid, or on the chocolate syrup sides.

of dehydroacetic acid. The wrapped loaves were stored for 7 days at 85 F. in an atmosphere having about per cent relative humidity. In external appearance the untreatedhontrol wrapped loaves had a heavy growth of black and bluegreen molds, on their outer crusts, especially along the side, just under the crown. The loaves wrapped in the commercial fungistatic sheet had healthy growths of similar molds along their The loaves wrapped with paper containsamples containing 0.03 per cent or more of de- 75 ing dehydroacetic acid showed no mold growth the crusts. Unsliced loaves, wrapped with the .per containing dehydroacetic acid, are kept ae from mold both externally and internally.

EXAllI-LI 9 Citrus fruits tend to develop blue-green molds, pecially on bruised surfaces, during shipment id storage. Various coatings and wrappers have en suggested and employed to overcome this oblem, but without the desired success. To termine the eilectiveness of dehydroacetic acid' r this purpose, lemons which had already been ipped cross-country were purchased in Michin, their skins were abraded to provide a fresh lund, the lemons were then dipped in an aque- LS synthetic rubber or elastomer latex and dried warm air. The so-coated fruit was sprayed .th a suspension of Penicillium digitatum spores. id was incubated in a moist chamber at a temrature favorable to mold development. Some the lemons had been dipped in a latex conini'ng no fungistat, while the rest were dipped a latex containing 2 per cent of dehydroacetic :id, based on the total dispersed solids. The uit which had no dehydroacetic acid in its coatg was badly molded within a week after inocution, while that which had this compound in coating remained free from mold for the seval weeks of its storage period.

EXAMPLE 10 It is a common practice to allow such products a fruit cake and plum pudding to age for from few months to a year or more before they are lten. Usually. such products are wrapped or lcked in a cloth bag, or in several layers of tper. Sometimes the package is sealed by imersion in molten paraflin wax. Regardless of [8 type of wrapping, it often happens that these 'oducts, in storage, become covered with mold. 'hile such mold may be merely superficial, it ,ay also strike into and spoi1 the wrapped od. Two means of protection have now been lund. In one method, 0.2.per cent of dehydro- :etic acid may be incorporated in the ingredients the fruit cake. or plum pudding before bakg or cooking, and mold growth on the wrapper Jes not penetrate into the packed product. In mother method, the wrapping material is imregnated with from 1 to 5 per cent and usually ot over 2 per cent by weight of dehydroacetic old, and is dried. The so-treated wrapper relains free from mold growth, even when stored nder conditions which foster mold grbwth on ntreated packages of the same materials.

In addition to the common carbohydrate food cntaminant organisms, specific examples of 'hich are named hereinabove, various bacterial ontaminants, some of which are pathogenic, may also be encountered in such foods, especialwhen the food is not handled under fully saniary conditions. It is desirable, of course, to imart to the food a resistance to the growth of uch organisms. It has been found that dehyroacetic acid has an antibacterial action on a ariety of pathogenic bacteria, in vitro. and it can e expected to make foods containing or coated Iith it more resistant to the proliferation of these acteria. The numerical values in the following able represent the concentration of antibacterial gent, in per cent by weight, required to inhibit ompletely the growth of the listed organisms in nutrient medium. For comparison, results are iven for dehydroacetic acid, and two other 1.4- yrone compounds, maltol and kojic acid, as the ntibacterial agents.

Antibacterial Agent Organism D h dr K I 8 Y 0 0 G acetic Acid Acid Staphylococcus damn 0. 4 2. 0 l. 0 Ebcrthclla typhoac" 0. 3 1.0 1. 0 Escherichia coll 0. 4 1.0 1.0 I Bacillus meamlcrlcus 0. 3 0. 6 1. 0 Alcaligmea ecalia. 0.3 0.3 0.3 Bacillus cu till: 0.3 1.0 1.0 Prcudomonaa aeroginom 0.3 2. 0 2.0 Salmonella pulloru'm 0.3 l.0 0.6 Staphylococcus hemolyticu 0. 3 0. 5 l. 0 Bacillus meaulhcrlu-m 0. 3 l. 0 i. 0 Baclllurcercua l i 0. 2 0. 5 0. 8

cent) of the weight of the food. In no case was the color, odor or taste of the food altered by the treatment.

The treatment of proteinaceous and fatty foods with dehydroacetic acid or its salts is the subject of our concurrently filed application, Serial No. 721,878. The use of the same agents in the treatment of light alcoholic beverages is disclosed and claimed in another of our concurrently filed applications, Serial No. 721,879. Antifungal wrapping sheets containing these agents form the subject matter of yet another application flied by us concurrently herewith, Serial No. 721,880.

We claim:

1. The method of imparting to foods rich in carbohydrates an increased resistance to attack by microorganisms which comprises bringing into contact with such foods a compound selected from the class consisting of dehydroacetic. acid and its sodium, potassium, ammonium and calcium salts.

2. The method of imparting to foods rich in carbohydrates an increased resistance to attack by microorganisms which comprises incorporating in the food a minor'but effective amount of a compound selected from the class consisting of dehydroacetic acid and its sodium. potassium. ammonium and calcium salts.

3. The method of imparting to foods rich in carbohydrates an increased resistance to attack by microorganisms which comprises applying to the surface of the food a minor but eilective amount of a compound selected from the class consisting of dehydroacetic acid and its sodium. potassium. ammonium and calcium salts.

4. The method of imparting to foods rich in carbohydrates an increased resistance to attack.

by microorganisms which comprises enclosing the food in a wrapper containing an effective amount of a material selected from the class consisting of dehydroacetic acid and its sodium, potassium, ammonium and calcium salts.

5. The method of imparting to'foods 'rich in carbohydrates an increased resistance to attack by microorganisms which comprises bringin dehydroacetic acid into contact with such foods.

6. The method of imparting to foods rich in carbohydrates an increased resistance to attack by microorganisms which comprises incorporating a minor but efiectiveamount of dehydroacetic acid in the food.

- 7. The method of imparting to foods rich in .carbohydrates an increased resistance to attack by microorganisms which comprises applying a minor but effective amount of dehydroacetic acid to the surface of the fogs.

8. The method 01' parting to ioods rich in carbohydrates an increased resistance to attack by microorganisms which comprises enclosin the food in a wrapper containing an effective amount 1 of dehydroacetic acid.

9. The method of imparting to breadstufis an increased resistance to attack by microorganisms which comprises bringing the breadstufls into contact with a minor but eflective amount 01' dehydroacetic acid.

10. The method of imparting to breadstufls an increased resistance to attack by microorganism which comprises incorporating. dehydroacetic acid in the dough before baking, in an amount sumcient to inhibit mold growth on the baked bread but insuflicient to prevent the unbaked bread from rising.

11. The method of imparting to breadstufls an increased resistance to attack by microorganisms which comprises enclosing the bread in a Wrapper containing an eflective amount,'up to about 5 per cent by weight of the wrapper, 01' a compound,

selected from the group consisting of dehydroacetic acid and its sodium. potassium, ammonium and calcium salts. r

12. A prepared food, containing at least per cent of carbohydrate based on the weight of food solids present, in contact with up to about 1 per cent of its weight of a compound selected from the class consisting of dehydroacetic acid and its sodium, potassium, ammonium and calcium salts.

13. As an article of manufacture, a raised and baked loaf of bread containing suflicient dehydroacetic acid to impart to the loaf resistance to the growth of microorganisms.

14. Baked bread, enclosed in a wrapper containing an antifungal amount, up to about 5 per cent of the weight ot'the wrapper, of dehydroacetic acid.

GERALD H. COLEMAN. PAUL A. WOLF.

REFERENCES CITED The following references are of record in the file of this patent:

OTHER. REFERENCES Ind. Eng. Chem, vol. 32, pages 16-22, 1940, article by A. B. Boese, Jr. s 

